1. Field of the Invention:
The present invention relates to an electrophotographic photoreceptor. More particularly, the present invention relates to an electrophotographic photoreceptor having very high sensitivity and performance, which has a photosensitive layer containing an organic photoconductive material.
2. Discussion of the Background
Heretofore, an inorganic photoconductive material such as selenium, cadmium sulfide or zinc oxide has been widely used in a photosensitive layer of an electrophotographic photoreceptor. However, the recovery of poisonous selenium and cadmium sulfide is required, and these compounds have various disadvantages that selenium is poor in heat resistance since it is crystallized by heat, that cadmium sulfide and zinc oxide are poor in moisture resistance, and that zinc oxide is poor in printing resistance. Thus, an effort for developing a novel photosensitive material is continued. Recently, an organic photoconductive material has been developed to be used as a photosensitive layer of an electrophotographic photoreceptor, and organic photoconductive materials have been practically utilized. As compared with an inorganic photoconductive material, an organic photoconductive material has advantages that it produces a light weight photosensitive material, that it is non-poisonous to environments, that it can be easily produced and that it can produce a transparent electrophotographic photoreceptor.
Recently, generation function and transportation function of a charge carrier are separated and born on respectively different compounds. Since such a function-separation type photosensitive material is effective for increasing sensitivity, this type is mainly developed and an organic photosensitive material for this type is practically utilized.
As a charge carrier-transporting medium, there are a case of using a high molecular photoconductive compound such as polyvinylcarbazole and a case of using a low molecular photoconductive compound dispersed and dissolved in a binder polymer.
Particularly, since an organic low molecular photoconductive compound is usable in combination with a binder polymer excellent in film formability, flexibility and adhesive property, a photosensitive material excellent in mechanical properties can be easily provided (see, for example, JP-A-60-196767, JP-A-60-218652, JP-A-60-233156, JP-A-63-48552, JP-A-1-267552, JP-B-3-39306, JP-A-3-113459, JP-A-3-123358 and JP-A-3-149560). However, it has been difficult to find a compound suitable for producing a highly sensitive photosensitive material.
Further, under continuous demand for high sensitivity, there are various problems that a residual potential is insufficient in view of electric properties, that a photo-responsiveness is poor, that a charge acceptance is lowered when used repeatedly, and that a residual potential is accumulated. In order to solve these problems, a technique for preventing the rise of a residual potential without impairing other properties of a photosensitive material by using, for example, two kinds of hydrazone compounds in combination, has been proposed (see JP-A-61-134767). However, well-balanced properties can not be always provided, and it is demanded to technically improve total properties of a photosensitive material in good balance.
Further, as a light source, a semiconductor laser is positively used in the field of a printer. In such a case, since the wavelength of the light source is in the vicinity of 800 nm, the development of a photosensitive material having a high sensitivity to a long wavelength light in the vicinity of 800 nm is strongly demanded.
As a material to satisfy this demand, there are reported such materials as disclosed in JP-A-59-49544, JP-A-59-214034, JP-A-61-109056, JP-A-61-171771, JP-A-61-217050, JP-A-61-239248, JP-A-62-67094, JP-A-62-134651, JP-A-62-275272, JP-A-63-198067, JP-A-63-198068, JP-A-63-210942, JP-A-63-218768, JP-A-62-36674, JP-A-7-36203, JP-A-6-110228, JP-A-6-11854, JP-A-63-48553, JP-A-62-139563, JP-A-2-154269 and JP-A-4-290851, and there are known various oxytitaniumphthalocyanines having a crystal type suitable as an electrophotographic photoreceptor material. However, further, there has been demanded an electrophotographic photoreceptor having a high sensitivity to a long wavelength light and satisfactory other electric properties. Also, the above patent publications do not disclose such a compound having substituents of the formula (2) and the formula (2') in the arylamine type compound having the formula (1), ##STR1## wherein each of R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 may be the same or different, and is a halogen atom, an alkyl group which may have one or more substituents, an alkoxy group which may have one or more substituents, an aryl group which may have one or more substituents or a substituted amino group;
each of k, l, m, n, o and p is an integer of from 0 to 4, and when the integer is two or more, a plurality of each of R.sub.1 to R.sub.6 may be the same or different; PA1 X.sub.1 has the formula (2); .paren open-st.CR.sub.7 .dbd.CR.sub.8 .paren close-st..sub.i --CR.sub.9 .dbd.CR.sub.10 R.sub.11 (2), and PA1 X.sub.2 has the formula (2'); .paren open-st.CR.sub.12 .dbd.CR.sub.13 .paren close-st..sub.h --CR.sub.14 .dbd.CR.sub.15 R.sub.16 (2') PA1 (wherein in the formulas (2) and (2'), i is an integer of from 1 to 4; PA1 h is an integer of from 0 to 4; PA1 each of R.sub.7, R.sub.8, R.sub.9, R.sub.10, R.sub.11, R.sub.12, R.sub.13, R.sub.14, R.sub.15 and R.sub.16 may be the same or different and is a hydrogen atom, an alkyl group which may have one or more substituents, an alkoxy group which may have one or more substituents, an aryl group which may have one or more substituents or a heterocyclic group which may have one or more substituents; PA1 a pair of R.sub.10 and R.sub.11 or a pair of R.sub.15 and R.sub.16 may be condensed to form a carbon-cyclic group or a heterocyclic group, provided that when one of the pair of R.sub.10 and R.sub.11 and the pair of R.sub.15 and R.sub.16 is a hydrogen atom or an alkyl group, the other is an aryl group or a heterocyclic group; PA1 when i is from 2 to 4, each of R.sub.7 and R.sub.8 may be the same or different; and PA1 when h is from 2 to 4, each of R.sub.15 and R.sub.16 may be the same or different; PA1 and these groups X.sub.1 and X.sub.2 may be the same or different). PA1 each of k, l, m, n, o and p is an integer of from 0 to 4, and when the integer is two or more, a plurality of each of R.sub.1 to R.sub.6 may be the same or different; PA1 X.sub.1 has the formula (2); .paren open-st.CR.sub.7 .dbd.CR.sub.8 .paren close-st..sub.i --CR.sub.9 .dbd.CR.sub.10 R.sub.11 (2), and PA1 X.sub.2 has the formula (2'); .paren open-st.CR.sub.12 .dbd.CR.sub.13 .paren close-st..sub.h --CR.sub.14 .dbd.CR.sub.15 R.sub.16 (2') PA1 (wherein in the formulas (2) and (2'), i is an integer of from 1 to 4; PA1 h is an integer of from 0 to 4; PA1 each of R.sub.7, R.sub.8, R.sub.9, R.sub.10, R.sub.11, R.sub.12, R.sub.13, R.sub.14, R.sub.15 and R.sub.16 may be the same or different and is a hydrogen atom, an alkyl group which may have one or more substituents, an alkoxy group which may have one or more substituents, an aryl group which may have one or more substituents or a heterocyclic group which may have one or more substituents; PA1 a pair of R.sub.10 and R.sub.11 or a pair of R.sub.15 and R.sub.16 may be condensed to form a carbon-cyclic group or a heterocyclic group, provided that when one of the pair of R.sub.10 and R.sub.11 and the pair of R.sub.15 and R.sub.16 is a hydrogen atom or an alkyl group, the other is an aryl group or a heterocyclic group; PA1 when i is from 2 to 4, each of R.sub.7 and R.sub.8 may be the same or different; and PA1 when h is from 2 to 4, each of R.sub.15 and R.sub.16 may be the same or different); PA1 and these groups may be the same or different.
When a hole moves to an adjacent charge-transporting material (CTM) molecule, the hole is liable to move to the highest occupied molecular orbital (HOMO) of the CTM molecule. HOMO of a molecule is widely distributed on a nitrogen atom and a double bonding .pi. electron connected therewith, and accordingly a CTM molecule having a larger number of HOMO is considered to be a material having a high hole-moving capacity. It is therefore considered that a molecule having a higher total number of .pi. electron number and lone electron number of nitrogen has a high hole-moving property. On the basis of this theory, various organic molecules have been studied, and it has been discovered that a molecule having a total amount W of .pi. electron number and lone electron number of nitrogen of CTM of at least 60 is a molecule having a very high hole-moving capacity.
The present invention has been made for solving the above-mentioned problems, and the first object of the present invention is to provide an electrophotographic photoreceptor having a high sensitivity and a high durability.
The second object of the present invention is to provide an electrophotographic photoreceptor having a high sensitivity and an excellent durability and also having advantages that a residual potential is sufficiently low even when a coating thickness is large and that properties do not change even when used repeatedly.
The third object of the present invention is to provide an electrophotographic photoreceptor having a high sensitivity to a long wavelength in the vicinity of 800 nm and also having satisfactory well-balanced properties in respect to charge acceptance, dark decay and residual potential.
The fourth object of the present invention is to provide an electrophotographic photoreceptor having a good responsiveness and a high carrier mobility.